Post-Passivation Interconnect Structure and Method of Forming the Same

ABSTRACT

A semiconductor device includes a passivation layer formed on a semiconductor substrate, a protective layer overlying the passivation layer and having an opening, an interconnect structure formed in the opening of the protective layer, a bump formed on the interconnect structure, and a molding compound layer overlying the interconnect structure and being in physical contact with a lower portion of the bump.

This application is a divisional of U.S. application Ser. No. 13/905,997, filed on May 30, 2013, entitled “Post-Passivation Interconnect Structure and Method of Forming the Same,” which claims priority to U.S. Provisional Application Ser. No. 61/747,136, filed on Dec. 28, 2012, entitled “Post-Passivation Interconnect Structure and Method of Forming the Same,” each application is hereby incorporated herein by reference.

BACKGROUND

Modern integrated circuits are made up of literally millions of active devices such as transistors and capacitors. These devices are initially isolated from each other, but are later interconnected together to form functional circuits. Typical interconnect structures include lateral interconnections, such as metal lines (wirings), and vertical interconnections, such as vias and contacts. Interconnections are increasingly determining the limits of performance and the density of modern integrated circuits. On top of the interconnect structures, bond pads are formed and exposed on the surface of the respective chip. Electrical connections are made through bond pads to connect the chip to a package substrate or another device. Bond pads can be used for wire bonding or flip-chip bonding. Flip-chip packaging utilizes bumps to establish electrical contact between a chip's input/output (I/O) pads and a substrate or lead frame of a package. Structurally, a bump actually contains the bump itself and an “under bump metallurgy” (UBM) located between the bump and the I/O pad. Wafer level chip scale packaging (WLCSP) is currently widely used because WLCSP is low cost and has relatively simple processes. In a typical WLCSP, post-passivation interconnect (PPI) lines such as redistribution lines (RDLs) are formed on passivation layers, followed by the formation of polymer films and bumps. A ball placement or a ball drop process is utilized in the WLCSP technology, but the ball drop performance is still a concern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-6 are cross-sectional views of a semiconductor device at various intermediate stages of a method of forming PPI structures on a semiconductor substrate in accordance with exemplary embodiments;

FIG. 7 is a plane view of the PPI structures in accordance with an exemplary embodiment; and

FIGS. 8-9 are cross-sectional views of a semiconductor device at various intermediate stages of a method of forming a bump on the PPI structure in accordance with exemplary embodiments.

DETAILED DESCRIPTION

The making and using of the embodiments of the disclosure are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the embodiments, and do not limit the scope of the disclosure. Embodiments described herein relate to the use of bump structures for use with semiconductor devices. As will be discussed below, embodiments are disclosed that utilize a bump structure for the purpose of attaching one substrate to another substrate, wherein each substrate may be a device, wafer, interposer substrate, printed circuit board, packaging substrate, or the like, thereby allowing for device-to-device, wafer-to-device, wafer-to-wafer, device or wafer to interposer substrate or printed circuit board or packaging substrate, or the like. Throughout the various views and illustrative embodiments, like reference numerals are used to designate like elements.

Reference will now be made in detail to exemplary embodiments illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. In the drawings, the shape and thickness may be exaggerated for clarity and convenience. This description will be directed in particular to elements forming part of, or cooperating more directly with, an apparatus in accordance with the present disclosure. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. Further, when a layer is referred to as being on another layer or “on” a substrate, it may be directly on the other layer or on the substrate, or intervening layers may also be present. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be appreciated that the following figures are not drawn to scale; rather, these figures are merely intended for illustration.

FIGS. 1-6 are cross-sectional views of a semiconductor device at various intermediate stages of a method of forming PPI structures on a semiconductor substrate in accordance with exemplary embodiments.

Referring first to FIG. 1, a semiconductor substrate 102 includes a substrate 10, an electrical circuitry 12, an inter-layer dielectric (ILD) layer 14, inter-metal dielectric (IMD) layers 16 and the associated metallization layers 18, 19 and 20.

A portion of the substrate 10 having electrical circuitry 12 formed thereon is shown, in accordance with some embodiments. The substrate 10 may comprise, for example, bulk silicon, doped or undoped, or an active layer of a semiconductor-on-insulator (SOI) substrate. The substrate 10 may be provided as a wafer level scale or a chip level scale. Other substrates, such as a multi-layered or gradient substrate may also be used.

Electrical circuitry 12 formed on the substrate 10 may be any type of circuitry suitable for a particular application. In some embodiments, the electrical circuitry 12 includes electrical devices formed on the substrate 10 having one or more dielectric layers overlying the electrical devices. Metal layers may be formed between dielectric layers to route electrical signals between the electrical devices. Electrical devices may also be formed in one or more dielectric layers. For example, the electrical circuitry 12 may include various N-type metal-oxide semiconductor (NMOS) and/or P-type metal-oxide semiconductor (PMOS) devices, such as transistors, capacitors, resistors, diodes, photo-diodes, fuses, and the like, interconnected to perform one or more functions. The functions may include memory structures, processing structures, sensors, amplifiers, power distribution, input/output circuitry, or the like. One of ordinary skill in the art will appreciate that the above examples are provided for illustrative purposes only to further explain applications of some illustrative embodiments and are not meant to limit the disclosure in any manner. Other circuitry may be used as appropriate for a given application.

The ILD layer 14 may be formed, for example, of a low-K dielectric material, such as phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), fluorinated silicate glass (FSG), SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers, silicon carbon material, compounds thereof, composites thereof, combinations thereof, or the like, by any suitable method, such as spinning, chemical vapor deposition (CVD), and/or plasma-enhanced CVD (PECVD). In some embodiments, the ILD layer 14 may comprise a plurality of dielectric layers. Contacts (not shown) may be formed through the ILD layer 14 to provide an electrical connection to the electrical circuitry 12.

One or more inter-metal dielectric (IMD) layers 16 and the associated metallization layers are formed over the ILD layer 14. Generally, the one or more IMD layers 16 and the associated metallization layers (such as metal lines 18 and vias 19) are used to interconnect the electrical circuitry 12 to each other and to provide an external electrical connection. The IMD layers 16 may be formed of a low-K dielectric material, such as FSG formed by PECVD techniques or high-density plasma CVD (HDPCVD), or the like, and may include intermediate etch stop layers. In some embodiments, one or more etch stop layers (not shown) may be positioned between adjacent ones of the dielectric layers, e.g., the ILD layer 14 and the IMD layers 16. Generally, the etch stop layers provide a mechanism to stop an etching process when forming vias and/or contacts. The etch stop layers are formed of a dielectric material having a different etch selectivity from adjacent layers, e.g., the underlying semiconductor substrate 10, the overlying ILD layer 14, and the overlying IMD layers 16. In some embodiments, etch stop layers may be formed of SiN, SiCN, SiCO, CN, combinations thereof, or the like, deposited by CVD or PECVD techniques.

In some embodiments, the metallization layers, including metal lines 18 and vias 19, may be formed of copper or copper alloys, or of other metals. Further, the metallization layers include a top metal layer 20 formed and patterned in or on an uppermost IMD layer to provide external electrical connections and to protect the underlying layers from various environmental contaminants. In some embodiments, the uppermost IMD layer is formed of a dielectric material, such as silicon nitride, silicon oxide, undoped silicon glass, and the like. In subsequent drawings, semiconductor substrate 10, electrical circuitry 12, ILD layer 14, and metallization layers 18 and 19 are not illustrated. In some embodiments, the top metal layer 20 is formed as a part of the top metallization layer on the uppermost IMD layer.

Thereafter, a contact pad 104 is formed and patterned to contact the top metal layer 20, or alternatively, electrically coupled to top metal layer 20 through a via. In some embodiments, the contact pad 104 may be formed of aluminum, aluminum copper, aluminum alloys, copper, copper alloys, or the like. One or more passivation layers, such as a passivation layer 106 are formed and patterned over the contact pad 104. In some embodiments, the passivation layer 106 may be formed of a dielectric material, such as undoped silicate glass (USG), silicon nitride, silicon oxide, silicon oxynitride or a non-porous material by any suitable method, such as CVD, PVD, or the like. The passivation layer 106 is formed to cover a peripheral portion of the contact pad 104, and to expose a central portion of the contact pad 104 through an opening in passivation layer 106. The passivation layer 106 may be a single layer or a laminated layer. In FIG. 1, a single layer of the contact pad 104 and the passivation layer 106 are shown for illustrative purposes only. As such, other embodiments may include any number of conductive layers and/or passivation layers.

Next, a first protective layer 108 is formed and patterned over the passivation layer 106. In some embodiments, the first protective layer 108 may be, for example, a polymer layer, which is patterned to form an opening 109, through which the contact pad 104 is exposed. In some embodiments, the polymer layer is formed of a polymer material such as an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), and the like, although other relatively soft, often organic, dielectric materials can also be used. The formation methods include spin coating or other methods. The first protective layer 108 has a thickness in a range between about 1 μm and about 10 μm. For example, a thickness between about 5 μm and about 8 μm.

Referring to FIG. 2, a second protective layer 112 is formed on the first protective layer 108 and fills the opening 109. Using photolithography and/or etching processes, the second protective layer 112 is patterned to form openings 113 a and 113 b exposing portions of the first protective layer 112 as depicted in FIG. 3. In some embodiments, the opening 113 a is formed in the second protective layer 112 over the contact pad 104 to expose the opening 109 of the first protective layer 108, and a portion of the first protective layer 108 adjacent to the opening 109 is also exposed by the opening 113 a. That is, the opening 113 a is positioned over the opening 109, and the opening 113 a has a diameter greater that that of the opening 109. The opening 113 a is a window on which one end of PPI structure will be fabricated in subsequent processes. In some embodiments, the opening 113 b is formed in the second protective layer 112 to expose other portions of the first protective layer 108. The opening 113 b is a window on which a landing pad region of PPI structure will be fabricated in subsequent process.

Next, as shown in FIG. 4, a first metallization layer 114 is formed on the resultant structure to cover the exposed portions of the contact pad 104, the first protective layer 108 and the second protective layer 112. The metallization layer 114 is formed so as to electrically connect to the contact pad 104. In some embodiments, the first metallization layer 114 includes at least one layer comprising titanium (Ti), tantalum (Ta), titanium nitride (TiN), tantalum nitride (TaN), copper (Cu), copper alloys, nickel (Ni), tin (Sn), gold (Au), or combinations thereof. In some embodiments, the first metallization layer 114 includes at least one Ti-containing layer and at least one Cu-containing layer. In an embodiment, the first metallization 114 includes a first portion 114 a and a second portion 114 b on which the PPI structure will be formed. The first portion 114 a is formed forms along the sidewalls and bottom of the openings 109 and 113 a, while the second portion 114 b is formed along the sidewalls and bottom of the opening 113 b.

Referring to FIG. 5, a photoresist layer 115 is provided on the metallization layer 114. Using photolithography process, the photoresist layer 115 is patterned to form openings 115 a and 155 b. In an embodiment, the opening 115 a exposes the first portion 114 a of the first metallization layer 114, while the opening 115 b exposes the second portion 114 b of the first metallization layer 114. In an embodiment, the patterned photoresist layer 115 stands over the patterned second protective layer 112. The position and diameter of the openings 115 a and 115 b are substantially the same as the openings 113 a and 113 b respectively.

Then as shown in FIG. 6, a second metallization layer 110 is formed in the openings 115 a and 115 b. In an embodiment, the second metallization layer 110 fills the openings 109, 113 a and 113 b. After removing the photoresist layer 115, exposed portions of the first metallization layer 114 on the surface of the second protective layer 112 are removed. This completes the formation of the second metallization layer 110 within the second protective layer 112. The second metallization layer 110 has a surface substantially planar with the surface of the second protective layer 112. In at least an embodiment, the second metallization layer 110 is a post-passivation interconnect (PPI) layer 110, which may also functions as power lines, re-distribution lines (RDL), inductors, capacitors or any passive components. In some embodiments, the PPI structure 110 includes copper, aluminum, copper alloy, or other mobile conductive materials using plating, electroless plating, sputtering, chemical vapor deposition methods, and the like. In some embodiments, the PPI structure 110 includes a copper layer or a copper alloy layer.

FIG. 7 is a plane view of the PPI structures 110 in accordance with an exemplary embodiment, and FIG. 6 is a cross-section view of the PPI structure 110 along line I-I of FIG. 7. The PPI structures 110 are formed in the second protective layer 112. Each illustrated PPI structure 110 includes a first region 110A, a second region 110B and a third region 110C. The first region 110A is one end of the PPI structure 110 formed over and electrically connected to the contact pad 104. The second region 110B is the other end of the PPI structure 110, functioning as a landing pad region on which a bump feature will be formed in subsequent processes. The third region 110C is a line region positioned between and electrically connecting the first region 110A and the second region 110B. It is experimentally observed in failure modes of pressure cooker test (PCT) and thermal cycle (TC) tests that the PPI structures 110 separated by the second protective layer 112 can prevent moisture attacking and reduce crack damage caused by liquid molding compound.

FIGS. 8-9 are cross-sectional views of a semiconductor device at various intermediate stages of a method of forming a bump on the PPI structure in accordance with exemplary embodiments.

Referring to FIG. 8, a bump 118 is formed on the second region 110B of the PPI structure 110. In an embodiment, the bump 118 is in physical contact with the PPI structure 110. The bump 118 can be a solder bump, a Cu bump or a metal bump including Ni or Au. In some embodiments, the bump 118 is a solder bump formed by attaching a solder ball to the second region 110B of the PPI structure 110 and then thermally reflowing the solder material. In an embodiment, the solder bump has a diameter greater than about 200 μm. In some embodiments, the solder bump includes a lead-free pre-solder layer, SnAg, or a solder material including alloys of tin, lead, silver, copper, nickel, bismuth, or combinations thereof. In some embodiments, the solder bump is formed by plating a solder layer using photolithography technologies followed by reflow processes.

Next, as shown in FIG. 9, a molding compound layer 116 is applied on the second protective layer 112, where the bump 118 is partially buried in the molding compound layer 116. In some embodiments, the molding compound layer 116 is in physical contact with a lower portion 118L of the bump 118, while an upper portion 118U of the bump 118 is exposed and protrudes from a top surface 116A of the molding compound layer 116. In some embodiments, a top portion 118T of the bump 118 is higher than the top surface 116A of the molding compound layer 116. The molding compound layer 116 may be in physical contact with the second protective layer 112 and/or the PPI structure 110. In some embodiments, a height (H1) of the bump 118 that is buried in the molding compound layer 116 may be between about ¼ to ¾ of a total height H2 of the bump 118. In at least one embodiment, the molding compound layer 116 is formed by applying a liquid molding compound and performing a curing process to cure and solidify the liquid molding compound. In some embodiments, a release film or a soft material may be applied on the liquid molding compound. Pressure is applied on the release film on the liquid molding compound, so that a portion of the bump 118 is pressed into release film. Furthermore, the pressure applied on the release film may push some of liquid molding compound downward. While the pressure is applied to the release film pushing against the bump and the liquid molding compound, a curing may be performed to cure and solidify liquid molding compound. After the solidification, the top portion 118T of the bump 118 is lower than the top surface 116A of molding compound layer 116. Thereafter, the release film is peeled off the molding compound layer 116, which is now in a solid form. The molding compound layer 116 residue remaining on the top portion 118T of the bump 118 is then etched. In the resulting structure, the molding compound layer 116 is formed with a portion of the bump 118 buried therein. After the bump formation, for example, an encapsulant may be formed, a singulation process may be performed to singulate individual devices 100 and wafer-level or device-level stacking or the like may be performed. Embodiments may be used in many different situations. For example, embodiments may be used in a device-to-device bonding configuration, a device-to-wafer bonding configuration, a wafer-to-wafer bonding configuration, device-level packaging, wafer-level packaging, or the like. In some embodiments, the semiconductor device 100 shown in FIG. 9 is flipped upside down and attached to another substrate, forming a package assembly.

The present embodiments provide PPI structures 110 formed in the protective layer 112, on which the bump 118 is formed and partially surrounded by the molding compound layer 116. The PPI structure 110 can prevent moisture attacking and reduce crack damage caused by molding compound layer 116. The molding compound layer 116 around the lower portion of the bump 118 can further enhance the thermal cycling life of the package assembly. Compared with other approaches of forming PPI structures within the molding compound layer, the present embodiments provide a method of forming the PPI structures 110 in the second protective layer 112 can achieve a low-cost structure without extra mask.

In accordance with an embodiment, a semiconductor device includes a passivation layer formed on a semiconductor substrate, a protective layer overlying the passivation layer and having an opening, an interconnect structure formed in the opening of the protective layer, a bump formed on the interconnect structure, and a molding compound layer overlying the interconnect structure and being in physical contact with a lower portion of the bump.

In accordance with another embodiment, a semiconductor device includes a contact pad on a semiconductor substrate, a polymer layer overlying the contact pad and the semiconductor substrate, a post-passivation interconnect (PPI) structure surrounded by the polymer layer, wherein the PPI structure comprises a first portion and a second portion, the first portion being electrically connected to the contact pad, a bump formed on and electrically connected to the second portion of the PPI structure, and a molding compound layer overlying the PPI structure and the polymer layer and being in physical contact with a lower portion of the bump.

In according with one aspect of the exemplary embodiment, a method of forming a semiconductor device, including: forming a passivation layer on a semiconductor substrate; forming a polymer layer overlying the passivation layer; forming an opening in the polymer layer; forming an interconnect structure in the opening of the polymer layer; forming a bump formed on the interconnect structure; and forming a molding compound layer surrounding the bump.

In the preceding detailed description, the disclosure is described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications, structures, processes, and changes may be made thereto without departing from the broader spirit and scope of the disclosure. The specification and drawings are, accordingly, to be regarded as illustrative and not restrictive. It is understood that the disclosure is capable of using various other combinations and environments and is capable of changes or modifications within the scope of inventive concepts as expressed herein. 

What is claimed is:
 1. A method of forming a semiconductor device, the method comprising: forming a passivation layer on a substrate; forming a polymer layer overlying the passivation layer; forming an opening in the polymer layer; forming an interconnect structure in the opening of the polymer layer; forming a bump formed on the interconnect structure; and forming a molding compound layer surrounding the bump.
 2. The method of claim 1, wherein an upper portion of the bump protrudes from a top surface of the molding compound layer.
 3. The method of claim 1, further comprising forming a metallization layer in the opening of the polymer layer before forming the interconnect structure.
 4. The method of claim 3, wherein the metallization layer extends from an uppermost surface of the polymer layer to a contact pad of the substrate.
 5. The method of claim 1, further comprising forming a contact pad on the substrate before forming the passivation layer, wherein the contact pad is partially covered by the passivation layer.
 6. The method of claim 5, further comprising forming a protective layer on the passivation layer before forming the polymer layer, wherein the protective layer comprises an opening exposing the contact pad.
 7. The method of claim 1, wherein the polymer layer comprises a first polymer layer and a second polymer layer over the first polymer layer.
 8. The method of claim 7, wherein the first polymer layer extends along sidewalls of the passivation layer along sidewalls of the opening.
 9. A method of forming a semiconductor device, the method comprising: forming a passivation layer over a substrate, the passivation layer having a first opening exposing a contact pad; forming a protective layer over the passivation layer, the protective layer comprising a first protective layer and a second protective layer, the first protective layer being a single layer and having a second opening, the first protective layer extending along an upper surface and sidewalls of the passivation layer, the first protective layer contacting the contact pad; forming a conductive layer in the first opening and the second opening, the conductive layer comprising a first material layer, the first material layer having a single composition, the first material layer extending from an upper surface of the second protective layer to the contact pad, an upper surface of the conductive layer being level with an upper surface of the second protective layer, the conductive layer having an entire top surface substantially co-planar with a top surface of the second protective layer; placing a bump directly on the conductive layer; and forming a molding compound layer in physical contact with the protective layer, the conductive layer and a lower portion of the bump.
 10. The method of claim 9, wherein a sidewall of the second protective layer adjacent to the conductive layer is substantially perpendicular to the top surface of the second protective layer.
 11. The method of claim 10, wherein a sidewall of the first protective layer adjacent to the contact pad is sloped relative to a top surface of the contact pad.
 12. The method of claim 9, wherein the conductive layer comprises a landing pad, an intermediate portion, and a contact region, wherein the contact region is interposed between the landing pad and the intermediate portion, wherein the bump directly contacts the landing pad.
 13. The method of claim 12, wherein the intermediate portion has a width less than a width of the contact region and a width of the landing pad.
 14. The method of claim 12, wherein a longitudinal axis of the landing pad is not aligned with the contact region.
 15. A method of forming a semiconductor device, the method comprising: forming a contact pad on a wafer scale substrate; forming a first protective layer over a contact pad, the first protective layer having a first opening exposing the contact pad, the first protective layer contacting the contact pad; forming a first polymer layer over the first protective layer; forming a second polymer layer over the first polymer layer, the first polymer layer and the second polymer layer having a second opening exposing the contact pad, the first polymer layer and the first protective layer being formed of different materials; after forming the second polymer layer, forming a post-passivation interconnect (PPI) structure in the second opening, wherein the PPI structure comprises a first layer extending from the contact pad to an upper surface of the second polymer layer; and forming a molding compound directly on the second polymer layer.
 16. The method of claim 15, wherein an upper surface of the PPI structure and the upper surface of the second polymer layer are level.
 17. The method of claim 15, wherein the PPI structure comprises a first portion, a second portion, and a third portion, the first portion being electrically connected to the contact pad, the first portion extending into the first opening, wherein the third portion electrically couples the first portion to the second portion, a width of the third portion being less than a width of the first portion and a width of the second portion in a plan view.
 18. The method of claim 17, wherein the first layer does not extend between the first portion and the second portion of the PPI structure.
 19. The method of claim 18, wherein the PPI structure comprises a second layer over the first layer, wherein the first layer comprises a different material than the second layer.
 20. The method of claim 15, wherein the molding compound is in direct contact with the PPI structure. 